The Hokkaido Pony (Do-San-Ko) (Equus caballus) is an old breed, a tough horse that have lived in Hokkaido for hundreds of years, and they have the ability to survive the harsh Hokkaido winters in the wild.  The Hokkaido horse is believed to have been brought to Hokkaido during the Edo period (1600-1867) by fishermen who used them as work horses and for transportation.  The fishermen would return to the Japanese mainland in autumn and would leave the horses in Hokkaido during winter unattended, leaving them to fend for themselves in the wild.  During the Edo period the Nanbu horse was thought to be inferior, and this is why the fisherman did not bring the horses back to the mainland.  Winter in Hokkaido is snowy, cold and harsh with little food for horses, but in the mountain regions of Hokkaido, bamboo grass can be found, and that was what the horses mainly ate.  In spring, the fishermen would return with new horses and would use the surviving horses.  The Hokkaido horse is a direct descendant of the Nanbu horse that were bred in the Tohoku region of Japan.  But the Nanbu breed no longer exists, and there is no definite info on its history.  This is due to the Nanbu horse being a military horse and was heavily crossbred in the late 19th century, in order to develop larger breeds for modern military.  
Most Do-San-Ko (Nanbu horses) are found in the eastern parts of Hokkaido.  In 1990, their numbers were over 2,500.  By 1995, their numbers had shrunk to closer to 2,000, and the data from a 2015 survey places their current number at just over 1,000 which means they are rare and becoming rarer.  Today, they are used as pleasure mounts and are great for inexperienced riders since these horses are mild tempered.  And they are great pack-work horses, used to transport gear into mountain regions of Hokkaido where trucks cannot be used, as they are very strong for their size.  They are commonly between 13 and 13.2 HH, or ‘hands high’, a measurement that equals approximately 4 inches (10 cm), so the average Do-San-Ko is between 52 and 53 inches (130-132 cm) in height.  They are also popular mounts for Yabusame (流鏑馬) the art of archery from horseback, that was common during Samurai battles.  The Mongolian horse is a close descendant to the Hokkaido horse, they are similar in height of 12 to 14 HH (48-56 inches or 122cm to 142 cm).  They weigh between 500 to 600 pounds, and can be used as workhorses for twenty years, their average life span is 40 years.